It is known in the art relating to small air compressors to use either of two different forms of crankcase and cylinder lubrication, oil mist and splash.
Oil misting is accomplished by injecting a metered amount of oil, such as through a one way check valve, into the compressor's crankcase. The turbulence in the crankcase caused by the spinning crankshaft and reciprocating piston breaks up the oil droplets, creating a fine mist. As the oil mist accumulates in the crankcase, the excess oil drops down to the sump or oil pan and is returned to an external reservoir through another check valve connected with the sump. The compressor crankcase has positive and negative pressure pulsations caused by the piston movement which pull in and push out oil through the two check valves.
A draw back of the oil mist oiling system is that when the compressor is shut down for several hours or days, all of the oil in the crankcase will drain out. Then, when the compressor is restarted, it may run for several cycles without adequate lubrication because of insufficient oil mist. Also, if the oil supply is cut off during operation, the compressor may soon fail from lack of lubrication. Advantages of the mist system are low oil consumption and avoidance of a need to maintain a particular crankcase oil level.
The splash system uses a crankcase with a sump or oil pan filled with oil and a dipper attached to or forming part of the connecting rod or crankshaft. As the crank rotates, the dipper picks up oil from the sump and splashes it over the inside of the crankcase, lubricating the bearings and piston of the compressor. This provides excellent lubrication. However, the system generally results in higher oil consumption than the mist system and requires that the oil level be regularly checked to see that it is properly maintained.